Potentiometer



Nov. 24, I964 F. E. DOLE 3,158,829

POTENTIOMETER Filed April 30, 1963. 2 Sheets-Sheet l 33 FIG.5 25

INVENTOR FRED E. DOLE ATTORNEYS F. E. DOLE POTENTIOMETER Nov. 24, 1964 2 Sheets-Sheet Filed April 50, 1965 FIG. [2

ZNVENTOR FR E D E. DOLE ATTORNEYS rllallllllllllld United States Patent Office 3358,8259 Patented Nov. 24, 1954 3,153,829 POTENTIOMETER Fred E. Dole, Rocky Hill, (Iona, assignor to Ace lEico tronics Associates, inc, a corporation of Massachusetts Filed Apr. 30, 1963, Ser. No. 276,825 Qlaims. (Cl. 338-488) The present invention relates to rheostats or potentiometers, and in particular it relates to an improved slider block for lead screw actuated rectilinear potentiometers or rheostats. I,

Generally, lead screw actuated rectilinear potentiometers comprise an elonagte housing within which is mounted an elongate resistance element, a lead screw, and a sliding contact. The sliding contact is mechanically coupled to the lead screw and also contacts the resistance element. These parts are arranged so that rotation of the lead screw causes a linear motion of the sliding contact along the length of the resistance element. Appropriate electrical input and output connections are made to the resistance element and the sliding contact to provide a voltage output for the unit which is related to the position of the contact element along the resistance element. j

In many precision potentiometer or rheostat units, the sliding contact is electrically isolated from the lead screw by means of an insulating slider block. The slider block is an element on which the sliding contact is mounted, and which provides the mechanical coupling to the lead screw to effect the linear traverse of the contact on rotation of the lead screw.

The linear traverse of the contact and slider block is of course limited by the extent of the lead screw. In the absence of special provisions, when the lead screw is turned to advance the slider to one end or the other of its extent, and if rotation were continued, the threaded coupling between the slider and lead screw would jam, and would be damaged. In precision otentiometers, and in other types as well, provision is usually made to enable the continued rotation of the lead screw, and to permit the slider to override the threads on the lead screw.

The present invention is concerned with this problem, and relates to a threaded coupling between the lead screw and slider assembly which permits this override, and permits a very great number of overriding revolutions without damage to the threaded coupling, while providing at the same time for accurate traverse tracking of the threads on the lead screw. In a general way, these results are accomplished by forming the slider insulation block and the rest of the potentiometer or rheostat in a manner that retains the slider non-rotationally oriented relative to the lead screw, and axially movable therealong. The slider insulation block is not per sethreadingly engaged with the lead screw, but rests on or is spaced outwardly from the crests of the lead screw thread. One or more resilient wires or rods are mounted in the slider block, andthese project therefrom and lie in. the thread grooves defined by the thread of the lead screw. This engagement between the screw thread and the projecting portions of the wires or rods aliords the threaded lead drive coupling for the slider block. When the block is driven to either end of its traverse, continued further rotation of the lead screw cannot move the block, and instead the wires or rods resiliently yield to the lead screw thread crests and override them without damage to the thread, the slider block, or the engaging wires or rods.

It is accordingly one object of the present invention to provide a slider for lead screw actuated potentiometers or rheostats.

Another object of the invention is to provide such a slider wherein the lead screw thread is yieldingly engaged by the slider, so as to permit override of the lead screw threads, on continued rotation of the lead screw when the slider reaches the limit of its traverse.

Another object of the present invention is to provide such a slider, wherein the threaded drive engagement with the lead screw is effected by one or more resilient wires g; rlclds yieldingly projecting from the body of the slider ther objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one specific exemplary embodiment thereof, had in' conjunction with the accompanying drawings, in which likenumorals refer to like or corresponding parts, and wherein:

FIG. 1 is a perspective view of a completed and assembled potentiometer unit embodying the present invention; L

FIG. 2 is a view of the potentiometer unit of FIG. 1, wherein the housing has been opened to show the interior of the unit in two parts;

FIG. 3 is a cross-sectional view of the potentiometer unit of FIG. 1, taken along the line 3-3 of FIG. 1, and the relation of this sectional view to FIG. 2 is indicated by the line 33 in FIG. 2; v I

FIG. 4 is an enlarged and detailed perspective view of the slider block used in the embodiment of FIGS. 1-3;

FIG. 5 is a cross-sectional view of the slider block taken along line 55 in FIG. 4; I bl FIG. 6 is an elevational view of the back of the slider ock;

FIG. 7, is a vertical sectional view of the slider block taken along line 7-7 in FIG. 6;

FIG. 8 is an elevational view of the back of the slider block, similar to FIG. 6, except the thread engaging rods or wires are inserted in place; I

FIGS. 9 and 10 are cross-sectional views of the slider as shown in FIG. 8, taken along the lines 9-9 and 1tll, respectively;

FIG. 11 is an enlarged anddetailed perspective view of the, slider contact element; and

FIG. '12 is an enlarged, fragmentary and detailed elevational View of the slider shown from the back and in position in the potentiometer unit of FIGS .,1 3,'particularly showing the engagement of the slider with thethreads of the lead screw;

The specific form of the slider herein described and shown was designed for use with the specific potentiometer described and claimed in my copending application S.N. 87,013, filed February 3, 1961, now Patent 3,090,025, issued May 14, 1963., That potentiometer is herein generally shown and described for background purposes, and for'further details reference is here made to said application.

The overall potentiometer unit comprises a molded plastic housing 26 formed from two mating parts 21 and 22. These parts are formed with transverse holes 23 and 24- therethrough so the unit can be readily positioned on appropriate mounting posts. Each housing part is formed with an interior recess. An elongate resistor 25, .shown as a wire wound resistance card, is cemented in the recess of housing portion 22. The remainder of the potentiometer mechanism is mounted in the recess of the outer housing portion 21.

Lead screw Zti is rotationally mounted adjacent one longitudinalside of the recess in housing portion 21, in suitable bearings which fix thescrew against axial and lateral movement. A conductive bus or slip bar 27 is located adjacent the opposite longitudinal side of the recess in housing portion 21, parallel to the lead screw '26 butlaterally offset from the lead screw to a point somewhat inward of the recess from the screw lti. A somewhat resilient slider block 28 is force fitted between the lead screw 26 and the bus 27, and because of the lateral offset relation of thelead screw and bus, the resilient force of the slider block functions to retain the bus in position against stops, now shown, which limit the movement ofthe businwardly of the recess. The slider block may be 'formed'of'a low friction plastic material, such for example as Teflon or nylon. A conductive slide contact unarmed to bemo'u'n'ted on the slider block 28, with one end33.contactingthe resistance element and the otherend 3'2'contactingthe busor slip bar 27.

The top edge'ofsliderblock 28'is formed with a groove or channel therealong having an arcuate cross-section whose radiusof curvature is about equal to the crest radius of the lead screw thread, so. that the groove 35 lies over. 'thethread. The front side of the block 23 is. formed with a recessed seat at 30, followed by a re- .eedin gjor tapering wedge shaped portion 34. The bottom edgeof the block 28; is provided with two depending feet 36 each defining arecessed portion 37. s

The block is assembled in the potentiometer by first positioning the arcuate channel 35 about the lead screw and then forcing thebottorn'of the block inwardly of the housing recess against bar 27 until the bottom of the block ,29 snaps. over the bar 27, embracing it in the recess 37. ,Since the block issizedto be resiliently force fitted between the :lead screw '26 and bar 27, the force exerted by the block'between the lead screw and the bar functions to retainthe ber position in the housing recess.

The, contact element 29 is seated on the block 28 by slipping its tail portion 32 between the taper 34 on the slider block andthe bus 27, and locating the reversely v bent fulcrum 3ll on the contact element the recessed seat 30. When the two housing parts 21 and 22 are then brought together, the contact tip 33 is caused to bear resilientIy against the resistance element 25, and through the bearing of the fulcrum 31, the tail portion 32 of the contact element is caused to bear resiliently against the bus or slip bar'27.

Appropriategrooves 51 are formed in one end of the heusin gjportions 21 andzlfonthe purpose of introducing wire leads into the housing 20 to makeeleetrical connections with the resistance element 25 and thebus 27.

nowdescr ibed. Two channels 38 and? are formed in the baekfside of the slider block The axes of these channelslie at an angle whichwould correspond to the pitch ofthe thread on the lead screw 26 when the slider block is inserted between the lead screw 26 and the bus 27. These channels varyin depth longitudinally, as shown in the sectional view of FIG. 7, to form curved bottom contours, andthey vary in width, as shown in FIG. 6, from narrow dimension portions 42 and 43 at the top, to relatively wide dimensionportions 40 and 41 for the remainder. Approximatelyat the longitudinal center of each channel 38, 39 a retaining or bearing bridge 44, stormed. a

Resilient wires or rods 48 and 49 are seated in the grooves 38 and 39, and their portions 52 protrude from the upper ends thereof into the channel 35. These wires or rods are preferably formed from a rather stiff but resilient grade. of spring metal. They are mounted in the slots 38 and 39 by being inserted in the bottom ends of the slots, being fednpwardly under the retaining bridges 44 and 45 and through the top portions of the slots until they protrude a desired distance into the channel 35preferably a distance equal to a little more than the radius of thechannel. Because of the retaining effect of bridges'44 and 45, the wires 48 and 49 follow the bottom curved contour of the slots even though the slots are otherwise open faced; and because of the resultant curvature of the wires and their inherent resilience, the protruding ends 52 are resiliently biased to offer a resistance to movement outwardly of the slots, and when so displaced, they exert a substantial returning force. A cement may be applied through apertures (wand 47 in the front face of the slider block 28 to insure that the wires 48 and 49 are not displaced axially along the slots 38 and 39.

As previously stated, the slots 38 and 39 are arranged at an angle to correspond with the pitch of the thread onthe lead screw when theslide'r block is inserted between the lead screw and the bus. Since the 'wires 48 and 49 occupy the sameangle, the portions 52 of the wires'pro- .trudingfinto thechannel 35 seat in the groovesSO formed by the lead screw thread, as shown in FIG. '12 In so seating, these ends of the wires are forced outwardly of their grooves somewhat against the resilient returning 'force or bias. The wires exert asufl icient returning force to track accurately in the grooves 50 'and'therebyform the threaded drive engagement between the slider and the lead screw.

Accordingly, jon rotation of lead screw 26, the ends 52 of wires 4% and 4.? cause a linear, traverse. of the slider block 28 and its associated contact element 29, causing the some tip 33 of element 29 to traverse the resistance element 251 while its tail portion 32 slides along the bus or slip bar '27., Whenthc slider assembly reaches the limit of travel in'eitherdirection along the lead screw, block 28 threadby the wires "4Sjand 49 withaminimum of play, 'the dinie'n'si'o'n otthe slots 46 and 41 at theupperfportions and '43 is'niade suhstantiallyequal toithat. of the Wires edandw'alongthe tracking line (ilejp'ar'allel to the lead :screw axis), while the perpendicular dimension of these portions ofthe slots 'is'made significantly greater to'acco'rninoda'te movement of the wires outwardly as'they seat in thethre'ad'grooves of the lead screw and when theyoverride'the' crests of the lead screw thread.

lOo'viously the principles of thepresentinvention are not limited to the specific'potentionieter unit herein shown and described forpurpo'sesof'illustration. For example, the shape of the grooves 38 and39 may be changed withbnt departing from the'scopc or" the present invention, and

lilrewise one or anyother number ofwir'es may be. used instead of the'two herein specifically suggested. 'Other 'mcditications'andvariations will alsobe apparent to those 'skillcd in, the art, and such asar e within the spiritla'n'd scope of the appei'rded claims are considered to be within the purview of the present invention.

.What is claimed is:

i. Ina potentiometer or rheostat'h'aving an elongate resista nceelement, a lead screw extending 'alongjsaid elemer t, a sl der assembly, means'for 're'stl'aining'said assembly against rotation about the lead screw axis, and'means th eadingly'coupling said assembly toisaid lead screw, whereby upon rotation of saidlead screwsaid assembly is' caused to traverse along said leadscrew'and resistance element; the improvement wherein'said slider assembly includes a block having one side located adjacent said lead screw and having an opening therein transverse to said side, and said coupling means comprises alength, of resilient wire located in'saidopening andhaving a'free'end portion projecting therefrom transversely to said side, said projectingportionbeing'pdsitioned in'the'g'roove of the lead screw defined bythescrew threadsthereof.

2. In a potentiometer or rheostat as set forth in claim l,

'the dimensions of said opening and wire at a point adjacent a greater than that of said wire along a line perpendicular a slip bar positioned in parallel spaced relation to said lead screw, a slider assembly fitted between said slip bar and lead screw, and a resistance element in parallel spaced relation to said screw and bar, said slider assembly includ-l ing a slider block mounted on said lead screw and bar for sliding movement therealong, a contact element carried by said block and engaging said resistance element and said bar, and meansfor threadingly coupling said block and said screw, said coupling means comprising a resilient length'of Wire mounted on said block and having a free end portion projecting therefrom, said projecting portion being positioned in the groove of the lead screw defined by the screw threads thereof.

5, A potentiometer or rheostat as set forth in claim 4, wherein said wire is embedded in, an opening in said block, said opening extending generally transversely of the axial direction of said lead screw.

6. A potentiometer or rheostat as set forth in claim 5, wherein the dimensions of said opening and wire at the point of emergence of said projecting portion from said block are substantially equal along a line parallel to the axis of said lead screw and that of said opening is greater than that of said wire along a line perpendicular tothe first line and to the axis of said wire, whereby said wire can move in the opening along said perpendicular line but is restrained against movement in said opening along said first line. r

7. A potentiometer as set forth in claim 6, wherein said opening is formed with a curvature along the axial dimension of said wire, and said block includes means for reraining said wire along said curvature to resiliently bias said wire against said movement along said perpendicular line. 1

8. A slider block for lead screw actuated potentiometers, comprising a block of insulation material, arsub stantially open sided slot formed in a first side of said block, one end of said slot being at a second side of said block located adjacent said first side, the bottom of said "slot having a generally concave curvature, a resilient length of Wire seated in said slot and having a free end projecting from said end of said slot, andrneans forretaining said wire against the curved bottom of said slot.

9. A slider block as set forth in claim 8, wherein the dimensions of said wire and said slot at said end are substantially equal along one line transverse to said wire and slot, and that of the slot is greater than that of the wire along another line transverse to said wire and slot.

10. A slider block as set forth in claim 9, wherein said greater dimension of said slot is along a line generally perpendicular to the plane of said first surface, and said equal dimension of said slot is along a line generally parallel to the plane of said first surface.

References Qited in the file of this patent 

1. IN A POTENTIOMETER OR RHEOSTAT HAVING AN ELONGATE RESISTANCE ELEMENT, A LEAD SCREW EXTENDING ALONG SAID ELEMENT, A SLIDER ASSEMBLY, MEANS FOR RESTRAINING SAID ASSEMBLY AGAINST ROTATION ABOUT THE LEAD SCREW AXIS, AND MEANS THREADINGLY COUPLING SAID ASSEMBLY TO SAID LEAD SCREW, WHEREBY UPON ROTATION OF SAID LEAD SCREW SAID ASSEMBLY IS CAUSED TO TRAVERSE ALONG SAID LEAD SCREW AND RESISTANCE ELEMENT; THE IMPROVEMENT WHEREIN SAID SLIDER ASSEMBLY INCLUDES A BLOCK HAVING ONE SIDE LOCATED ADJACENT SAID LEAD SCREW AND HAVING AN OPENING THEREIN TRANSVERSE TO SAID SIDE, AND SAID COUPLING MEANS COMPRISES A LENGTH OF RESILIENT WIRE LOCATED IN SAID OPENING AND HAVING A FREE END PORTION PROJECTING THEREFROM TRANSVERSELY TO SAID SIDE, SAID PROJECTING PORTION BEING POSITIONED IN THE GROOVE OF THE LEAD SCREW DEFINED BY THE SCREW THREADS THEREOF. 